A major challenge in engine oil formulation is simultaneously achieving wear control, and friction reduction, while also maintaining fuel economy performance, over a broad temperature range.
Lubricant-related wear control is highly desirable due to increasing use of low viscosity engine oils for improved fuel efficiency. As governmental regulations for vehicle fuel consumption and carbon emissions become more stringent, use of low viscosity engine oils to meet the regulatory standards is becoming more prevalent. At the same time, lubricants need to provide a substantial level of wear protection and friction reduction due to the formation of thinner lubricant films during engine operation. As such, use of antiwear additives and friction modifiers in a lubricant formulation is the typical method for achieving wear control and friction reduction. Due to limitations of using high levels of antiwear and friction modifier additives such as catalyst poisoning and deposit formation, it is highly desirable to find alternative methods for achieving excellent wear control and friction reduction without poisoning the catalyst.
Developing more effective additive package in combination with balancing lubricant viscosity has proven to be a successful and cost-effective route to improving engine efficiency and durability. Commercial lubricants are composed of base stock and several categories of additives including anti-wear, friction modifier, viscosity modifier, antioxidant, detergent, dispersant, etc. Specifically, friction modifiers and anti-wear agents play key role in reducing boundary and mixed friction and wear in engine locations such as the top-ring-reversal region of the piston ring-cylinder liner interface and sliding surfaces in the valve train. Furthermore, an effective anti-wear additive allows using a low viscosity lubricant, consequently reducing elasto-hydrodynamic friction loss.
PAOs are important lube base stocks with many excellent lubricant properties, including high viscosity index (VI), low volatility and are available in various viscosity range (Kv100 2-300 cSt). However, PAOs are paraffinic hydrocarbons with low polarity. This low polarity leads to low solubility and dispersancy for polar additives or sludge generated during service. To compensate for this low polarity, lube formulators usually add one or multiple polar co-base stocks. Ester or alkylated naphthalene (AN) is usually present at 1 wt. % to 50 wt. % levels in many finished lubricant formulations to increase the fluid polarity which improves the solubility of polar additives and sludge.
There is a need for base stocks or multifunctional fluids with better properties and the lube products with differentiation features. Ionic liquids (ILs) have been an active are of research at various universities, government labs and companies. ILs are effective lube additives but have known disadvantages (e.g., toxicity, high cost, limited range of available raw materials, and purity difficulties).
Despite advances in lubricant oil formulation technology, there exists a need for an engine oil lubricant that effectively improves wear control while maintaining or improving fuel efficiency. In addition, there exists a need for an engine oil lubricant that effectively improves wear control and friction reduction while maintaining or improving fuel efficiency.